1. Field of the Invention
The invention relates to methods and apparatus for determining a gas turbine engine generally ring-shaped dampening cone inner diameter. More particularly the invention also relates to methods and apparatus for determining the inner diameter of dampening cones having spherical or other convex inner diameter surface profiles.
2. Description of the Prior Art
Dampening cones are ring-shaped components that are interposed radially and axially between a gas turbine engine rotor tie rod and turbine disc rows to couple each row sequentially along the rotor and to maintain radial concentricity between the disc row/rotor tie rod interfaces. Due to the large diameter, axial length and rotating mass of gas turbine engines dampening cones must be precision machined with concentric inner diameters of uniform radius within tolerance specifications within tens of microns, in order to minimize rotating machinery vibration. The dampening cones often have spherical or other convex inner diameter profile surfaces, to establish a constant radius circular linear abutting contact relationship with the rotor tie rod at the peak inner surface diameter. In FIGS. 1 and 2, the gas turbine engine 10 has a rotatively mounted rotor tie rod 12 upon which are mounted adjoining, axially opposed turbine discs 14 and 16 that form corresponding turbine rows. The upstream turbine disc 16 defines a turbine disc groove 17, while the downstream turbine disc 14 defines a turbine disc shoulder 15.
As can be seen more clearly in FIGS. 2 and 4, ring-shaped dampening cone 20 defines a spherical, convex inner diameter surface 22 of relatively large radius R. The spherical radius high point 23 establishes a tangential circular line contact that circumscribes the rotor tie rod 12 and establishes the inner diameter D1. The dampening cone 20 also forms an annular lip 24 of inner diameter D2 that engages axially within the mating turbine disc groove 17. A shoulder 15 formed in the adjoining opposed turbine disc 14 abuts the dampening cone 20 outer surface both axially and radially to lock the dampening cone in fixed position relative to the turbine discs 14 and 16.
A known apparatus and method for determining dampening cone 20 inner diameters D1 and D2 is by interposing an inside micrometer across the cone surfaces forming those ring diameters. Given the relatively small tolerance variances of only tens of microns compared to ring inner diameters in the 100+ millimeter range, small tilt deviations from the true geometric where the inside micrometer ends contact the opposed ring diameter surfaces will lead to incorrect diameter readings. Correct inside micrometer orientation is also impacted by the experience of the machinist who is performing the measurements. Thus repeatable and consistent diameter determination is subject to variances in micrometer placement and individual inspector skill.
Thus, a need exists for a method and apparatus for accurately determining inside diameter of a ring-shaped gas turbine dampening cone, including dampening cones with spherical convex inside diameter profiles.
Another need exists for a method and apparatus for accurately determining whether an inside diameter of a ring-shaped gas turbine dampening cone is within component structural specifications and tolerances.
An additional need exists for a method and apparatus that facilitates determination of inside diameter of a gas turbine dampening cone with consistent inspection repeatability by an individual inspector and other human inspectors.